Reality cannot be found except in One single source, because of the interconnection of all things with one another. I maintain also that substances, whether material or immaterial, cannot be conceived in their bare essence without any activity, activity being of the essence of substance in general.
Gottfried LeibnizEither there are no corporeal substances, and bodies are merely phenomena which are true or consistent with each other, such as a rainbow or a perfectly coherent dream, or there is in all corporeal substances something analogous to the soul.
Gottfried LeibnizI do not believe that a world without evil, preferable in order to ours, is possible; otherwise it would have been preferred. It is necessary to believe that the mixture of evil has produced the greatest possible good: otherwise the evil would not have been permitted. The combination of all the tendencies to the good has produced the best; but as there are goods that are incompatible together, this combination and this result can introduce the destruction of some good, and as a result some evil.
Gottfried Leibniz